<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>JS/CSS 带图标手风琴动画效果</title>
    <style>
        button.accordion {
            background-color: #eee;
            color: #444;
            cursor: pointer;
            padding: 18px;
            width: 100%;
            border: none;
            text-align: left;
            outline: none;
            font-size: 15px;
            transition: 0.4s;
        }

        button.accordion.active,
        button.accordion:hover {
            background-color: #ddd;
        }

        button.accordion:after {
            content: '\002B';
            color: #777;
            font-weight: bold;
            float: right;
            margin-left: 5px;
        }

        button.accordion.active:after {
            content: "\2212";
        }

        div.panel {
            padding: 0 18px;
            background-color: white;
            max-height: 0;
            overflow: hidden;
            transition: max-height 0.2s ease-out;
        }
    </style>
</head>

<body>
    <h2>带图标手风琴</h2>
    <p>该实例选项添加了 “+” 号图标与 “-” 号图标。</p>
    <button class="accordion">选项 1</button>
    <div class="panel">
        <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et
            dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex
            ea commodo consequat.</p>
    </div>

    <button class="accordion">选项 2</button>
    <div class="panel">
        <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et
            dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex
            ea commodo consequat.</p>
    </div>

    <button class="accordion">选项 3</button>
    <div class="panel">
        <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et
            dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex
            ea commodo consequat.</p>
    </div>
    <script>
        var acc = document.getElementsByClassName("accordion");
        var i;

        for (i = 0; i < acc.length; i++) {
            acc[i].onclick = function () {
                this.classList.toggle("active");
                var panel = this.nextElementSibling;
                if (panel.style.maxHeight) {
                    panel.style.maxHeight = null;
                } else {
                    panel.style.maxHeight = panel.scrollHeight + "px";
                }
            }
        }
    </script>
</body>

</html>